Study of the antifungal activity of Acinetobacter baumannii LCH001 in vitro and identification of its antifungal components

Abstract

An Acinetobacter strain, given the code name LCH001 and having the potential to be an endophytic antagonist, has been isolated from healthy stems of the plant Cinnamomum camphora (L.) Presl, guided by an in vitro screening technique. The bacterium inhibited the growth of several phytopathogenic fungi such as Cryphonectria parasitica, Glomerella glycines, Phytophthora capsici, Fusarium graminearum, Botrytis cinerea, and Rhizoctonia solani. Biochemical, physiological, and 16S rDNA sequence analysis proved that it is Acinetobacter baumannii. When the filtrate from the fermentation broth of strain LCH001 was tested in vitro and in vivo, it showed strong growth inhibition against several phytopathogens including P. capsici, F. graminearum, and R. solani, indicating that suppression of the growth of the fungi was due to the presence of antifungal compounds in the culture broth. Moreover, the antifungal activity of the culture filtrate was significantly correlated with the cell growth of strain LCH001. The active metabolites in the filtrate were relatively thermally stable, but were sensitive to acidic conditions. Three antifungal compounds were isolated from the culture broth by absorption onto macropore resin, ethanol extraction, chromatography on silica gel or LH-20 columns, and crystallization. The structures of the bioactive compounds were identified by spectroscopic methods as isomers of iturin A, namely, iturin A2, iturin A3, and iturin A6. The characterization of an unusual endophytic bacterial strain LCH001 and its bioactive components may provide an alternative resource for the biocontrol of plant diseases.

Prokaryote–eukaryote interactions identified by using Caenorhabditis elegans

“…However, we were unable to demonstrate this by using an A. baumannii mutant defective in the production of 3-hydroxy-C 12 homoserine lactone (abaI::K m ) (21) and a range of synthetic AHL molecules with varying carbon-length backbones. The production of another cell-density-dependent compound is also a possibility, as has been shown for an environmental strain of Acinetobacter toward phytopathogenic fungi, which produced iturin A (20). In our study, iturin A was not effective at inhibiting C. albicans filamentation in C. elegans up to a concentration of 5 M. Given the therapeutic potential of our findings, further work to identify the active compound in A. baumannii supernatant is ongoing.…”

“…1B). Supernatant from an environmental strain of A. bau- mannii was recently identified as having antifungal activity (20). Isomers of iturin A were identified as the active molecules.…”

Characterization and Fungal Inhibition Activity of Siderophore from Wheat Rhizosphere Associated Acinetobacter calcoaceticus Strain HIRFA32

“…They are commonly found in rhizosphere of wheat [1,3,16,17]. These rhizospheric Acinetobacter strains exhibit PGB traits such as production of indole acetic acid [1], mineral solubilization [3], nitrogen fixation [18], antimicrobial activity [19] and synthesis of siderophores [2,3,18]. However, there is paucity of information on structure and role of siderophore from Acinetobacter found to be associated with rhizosphere of crop plant such as wheat.…”

Characterization of selected Gram-negative non-fermenting bacteria isolated from honey bees (Apis mellifera carnica)

“…A. pullulans and P. agglomerans are commonly found in honey bee's environment (Loncaric et al 2008(Loncaric et al , 2009). There are also other bacteria found in the honey bee environment including members of Burkholderia (Palumbo et al 2007), Acinetobacter (Evans and Armstrong 2006;Liu et al 2007), Pseudomonas (de Werra et al 2008), and Stenotrophomonas (Eva ns a nd Ar mstr on g 20 0 6; Romanenko et al 2008) that exhibit antagonistic activity against several different pathogens such as mycotoxigenic fungi or P. larvae.…”